1. Field of the Invention
Apparatuses consistent with the present invention relate generally to a fuel supply device for direct methanol fuel cells and more particularly, to a fuel supply device for direct methanol fuel cells comprising a cavity and a thin film type active pump and nozzles so as to actively supply a liquid fuel in a predetermined amount by receiving a signal from an external circuit.
2. Description of the Related Art
Recently, as use of notebooks, mobile phones, and PDAs is universalized, concern for energy sources of such portable electronic equipment or devices is increased. The cells used for portable electronic devices are required to be small-sized as the devices are miniaturized and to have a long usable time by a single supply. To meet these requirements, various types of cells have been developed.
Among the developed cells, fuel cells are of particular interest since they advantageously have a higher energy density per unit area, as compared to the conventional secondary cells, and can be used for a longer period of time by a single charge, as compared to the conventional cells. Also, since the fuel cells can maximize mobility of charging methods and be used semi-permanently, they are environmentally friendly energy sources which are expected to greatly contribute to the recent trend to make electronic devices portable, and slim and light.
The fuel cells are classified by fuel types, operation temperature, catalyst and electrolyte types, including for example, a phosphoric acid fuel cells (PAFC), alkaline fuel cells (AFC), polymer electrolyte fuel cells (Proton Exchange Membrane Fuel Cell, PEMFC), molten carbonate fuel cells (MCFC), solid oxide fuel cells (SOFC), direct methanol fuel cells (DMFC).
The direct methanol fuel cells are characterized by bringing about a chemical reaction to generate energy at room temperature. Also, they are advantageous in that they do not need a separate high performance apparatus for storing hydrogen since hydrogen is supplied from the liquid fuel.
The recharge of the fuel is simply accomplished by carrying or mounting a methanol capsule. Therefore, they can improve mobility.
As shown in FIG. 1, the direct methanol fuel cells comprise a membrane electrode assembly that includes an anode 2, a membrane 1 and a cathode 3. In the anode 2, the methanol reacts with water to produce hydrogen ions and electrons. Such reaction is shown in the following Reaction Scheme (I).CH3OH+H2O→CO2+6H++6e−  Reaction Scheme I
In the cathode 3, the hydrogen ions produced in the anode 2 are transferred through the membrane and binds to oxygen along with electrons to produce water. The reaction is as follows.1.5O2+6H++6e−→3H2O  Reaction Scheme II
The overall chemical reaction in the fuel cell is shown in Reaction Scheme III.CH3OH+1.5O2→CO2+2H2O, E0=1.18 V  Reaction Scheme III
As described above, the direct methanol fuel cells convert the energy generated in the overall chemical reaction to electrical energy and supply the converted energy to an electronic device.
The energy is generated by the chemical reaction of hydrogen ions from the methanol, which is properly supplied, with oxygen ions in the air. Typically, a mixture of methanol and water is used to obtain a needed amount of hydrogen. Here, if a methanol mixture at a high concentration is excessively supplied, a surplus methanol mixture passes through a membrane of the fuel cell without reaction (cross-over phenomenon), causing rapid deterioration in the efficiency of the fuel cell.
Also, the energy generation should be controlled in accordance with the operation mode of a small-sized electronic device, for example, the on mode, off mode and standby mode. For this, it is necessary to control the supplied amount of the liquid fuel.
Thus, there is a demand for an intellectualized fuel supply system applicable in small sized portable electronic devices which can actively control the liquid methanol in accordance with the conditions and environments in which the electronic devices are used.